1. Field
Aspects of the present disclosure relate generally to wireless communication systems, and more particularly, to scheduling of uplink transmissions in the presence of HARQ retransmissions in an uplink MIMO system.
2. Background
Wireless communication networks are widely deployed to provide various communication services such as telephony, video, data, messaging, broadcasts, and so on. Such networks, which are usually multiple access networks, support communications for multiple users by sharing the available network resources. One example of such a network is the UMTS Terrestrial Radio Access Network (UTRAN). The UTRAN is the radio access network (RAN) defined as a part of the Universal Mobile Telecommunications System (UMTS), a third generation (3G) mobile phone technology supported by the 3rd Generation Partnership Project (3GPP). The UMTS, which is the successor to Global System for Mobile Communications (GSM) technologies, currently supports various air interface standards, such as Wideband-Code Division Multiple Access (W-CDMA), Time Division-Code Division Multiple Access (TD-CDMA), and Time Division-Synchronous Code Division Multiple Access (TD-SCDMA). The UMTS also supports enhanced 3G data communications protocols, such as High Speed Packet Access (HSPA), which provides higher data transfer speeds and capacity to associated UMTS networks.
As the demand for mobile broadband access continues to increase, research and development continue to advance the UMTS technologies not only to meet the growing demand for mobile broadband access, but to advance and enhance the user experience with mobile communications.
For example, recent releases of 3GPP standards for UMTS technologies have included multiple input multiple output (MIMO) for downlink transmissions. MIMO can enable increased throughput in a transmission without requiring a commensurate increase in spectrum use, since two streams can be transmitted in the same carrier frequency, where they are separated by the spatial dimension by being transmitted from spatially separate antennas. In this way, an effective doubling of spectral efficiency can be achieved by transmitting dual transport blocks per transmission time interval.
Further, recent attention within the 3GPP standards body has been directed to a particular uplink beamforming transmit diversity (BFTD) scheme for high speed packet access (HSPA) networks within the UMTS standards, where a mobile terminal utilizes two transmit antennas and two power amplifiers for uplink transmissions. This scheme, when implemented in a closed loop mode under network control, has shown significant improvement in cell edge user experience, as well as overall improvements in system performance. However, in schemes that have been investigated, the mobile terminal has been limited to single stream transmissions across the two antennas.
Therefore, to increase the throughput and spectral efficiency for uplink transmissions, there is a desire to implement MIMO for uplink transmissions such that dual transport blocks can be transmitted in the same carrier frequency during the same transmission time interval.